The present invention relates to the handlebar of bicycle and more particularly to a twist handlebar which is rotatably to adjust the tensions of the deraileur and precisely controls the speeds of the bicycle by a stable displacement of a positioning device in the handlebar.
A stable controlling system provides a precise operation of the derailleur of a bicycle, thus an optimum design of a handlebar for a bicycle equiped with derailleurs is very important. A typical twist handlebar of bicycle as shown in FIGS. 1 and 2 comprises a housing 10 of a rotatable handle including an arcuate retaining plate 11 which has a slot 121 abutting a bore 122 in an inward extension 12 for gripping a large diameter end of a cable 13 which has another end extending out of the housing 10 via a thru hole 14 and connected to a derailleur of a bicycle, and a plurality of positioning slots 15 continuously formed in an inner periphery opposite to the extension 12, a stationary ring 20 fixedly secured to a base of the handlebar and including a first and second projections 21 and 22 for securing a roughly U-shaped spring plate 24 which has an inverse first end 25 displaceably engaging with the positioning slots 15 and a transverse extension 23 laterally extended from the second projection 22 so as to define a receiving space therein for disposing a bent second end 26 of the spring plate 24. When the handlebar twists clockwise or counterclockwise, the retaining plate 11 moves in concert with the handlebar and its positioning the first end 25 of the spring plate 24 under friction so that the tension of the derailleur through the cable 13 are variable.
However, the structure of this handlebar is designed under the concept of friction which is substantially an unstable design. Because the structure stability of this handlebar is effected by the resilience of the spring in the derailleur, therefore, if the first end 25 of the spring plate 24 is displaced to a rightmost positioning slot 15 (as shown in FIG. 1), the structure becomes unstable because of that the resilience of the spring becomes greater. If method is made to improve the stability by increasing the friction between the spring plate 24 and the slot 15, it requires greater returning torque when the spring plate 24 engages with leftmost positioning slot 15 and this handlebar will become more difficult to operate for it relies upon skillfully manual operation. Further, the first end 25 of the spring plate 24 has a bevel outer surface (as shown in FIG. 2) which has a tangent line defines a positive angle (+.theta.) relative to the tangent line of the inner surface of the positioning slots 15. This proves that the bevel surface facilitates a ready displacement but sacrifies a positional stability between the first end 25 and the slots 15.